British police are investigating how an intruder breached the walls of the Tower of London and stole a set of keys from the tourist attraction and home of the crown jewels.

Locks to the Tower's drawbridges and other rooms have been changed after a man was caught trespassing in the early hours of November 6 and escorted from the premises, according to a royal palaces statement.

See Also

The stolen keys did not provide access to the Tower itself, Historic Royal Palaces said in a statement, but admitted a lapse in security.

"Our well-established security systems and procedures are robust. However on this occasion, these procedures were not carried out to the expected standard," it said.

The Tower was begun by William the Conqueror in the 1080s and has been used by British monarchs as a home, place of execution and a prison for traitors ever since. Henry VIII had Anne Boleyn executed here.

The crown jewels on display at the palace include a solid gold crown weighing over 2 kg and the 105 carat Koh-i-Nur ("Mountain of Light") diamond.

A police spokesman said the incident was under investigation.

The Tower is traditionally staffed by ceremonial custodians, known as Yeoman Warders (nicknamed "Beefeaters"), former members of the British armed forces whose elaborate scarlet and gold tunics are one of the best known symbols of the capital.

The warders give tours and carry out the Ceremony of the Keys, the traditional locking up of the Tower of London that has taken place on each and every night, without fail, for at least 700 years and is a popular tourist attraction.

A young warder foiled a more audacious theft in 1671, when a gang of thieves attempted to make off with the crown jewels by smuggling them out under the cloaks and down their trousers.